Generally, mobile communications systems are made up of a plurality of cells. Each cell provides a radio communications center through which a mobile station establishes a call or other communications session with another mobile station or a terminal connected to either a circuit-switched network (e.g., public-switched telephone network or PSTN) or a packet-switched data network. Typically, each cell includes a radio base station, with each base station coupled to a switching center that controls processing of calls or other communications sessions between or among mobile stations or between mobile stations and terminals connected to a circuit-switched or a packet-switched network.
Various wireless protocols exist for defining communications in a wireless network. One type of protocol is based on the time-division multiple access (TDMA) technology, such as the TIA/EIA-136 standard or the Global System for Mobile (GSM) standard. Another type of protocol for wireless communications is based on the code-division multiple access (CDMA) technology. CDMA is a spread spectrum wireless communications protocol in which transmission is based on the spread spectrum modulation technique to allow many users to have access to the same band of carriers. Examples of other protocols include UMTS (Universal Mobile Telecommunications System) protocols (based on wideband CDMA), and the MCDV (multi-carrier data-voice) protocol that has been proposed by Nortel Networks.
Traditionally, wireless networks were designed for carrying circuit-switched voice traffic. However, with the wide availability of the Internet and intranets, packet-switched communications (e.g., web browsing, electronic mail, instant messaging, electronic gaming, and so forth) have become common. As a result, third generation (3G) and beyond wireless technologies are being developed to provide higher bandwidth and more efficient packet-switched communications (of data as well as voice and other forms of real-time data) over wireless networks.
Packet-switched wireless communications protocols have been developed for both TDMA and CDMA. For example, in the CDMA context, a CDMA 2000 family of standards has been developed that is capable of supporting both traditional circuit-switched traffic as well as packet-switched traffic.
The first phase of CDMA 2000 is referred to as 1×RTT (also referred to as 3G1× or 1×), which is designed to increase voice capacity as well as to support data transmission speeds that are faster than typically available. In addition, for even higher data rates in packet-switched communications, a High Rate Packet Data (HRPD) wireless technology has been developed. HRPD is defined as TIA/EIA/IS-856, “CDMA 2000, High Rate Packet Data Air Interface Specification,” which is adopted by the TIA. The HRPD technology is also referred to as the 1×EV-DO or 1×EV technology. 1×EV-DO provides relatively high data transfer rates over the air interface between mobile stations and base stations (usually faster than 1×RTT rates).
As demands for packet-switched services increase, including requirements for higher data speeds, hybrid systems may be used in which two or more technologies are implemented in a given cell or cell sector. For example, a wireless network can use a hybrid system in which both 1×RTT and 1×EV-DO technologies are implemented. Generally, 1×EV-DO provides higher data speeds than those offered by 1×RTT. Even with such hybrid systems, under heavy traffic conditions, one or the other system (e.g., either the 1×EV-DO system or the 1×RTT system) may become overloaded, which reduces the bandwidth available to mobile stations in the wireless network.